High-frequency discharge pumped laser device

ABSTRACT

A high-frequency discharge pumped laser device for producing a laser oscillation through application of a high-frequency voltage to a discharge tube, which includes a plurality of tube segments constituting the discharge tube, means for passing a laser gas axially through each of the tube segments, high-frequency power supplies for supplying a high-frequency voltage to the tube segments to generate a laser beam output, and a partition wall made of an electroconductive material and arranged between adjacent tube segments, the potential of the partition wall being maintained at a constant level. As the potential of the partition wall is maintained at a constant level, a mutual current caused by a stray capacity between the tube segments is eliminated, and thus fluctuation of the laser beam output is reduced.

TECHNICAL FIELD

The present invention relates to a high-frequency discharge pumped laserdevice with a high-power output for use in cutting workpieces of metalor the like, and more particularly, to a high-frequency discharge pumpedlaser device capable of stable high-frequency discharge pumping.

BACKGROUND ART

High-frequency discharge pumped axial-flow lasers are now used for avariety of applications, due to advantages such as a high-power output,high-quality beam, stable oscillation, high-speed control capability andthe like.

A conventional axial-flow type high-frequency discharge pumped laserdevice is illustrated in FIG. 6. In FIG. 6, numeral 1 denotes adischarge tube, which comprises four tube segments in the illustrationbut may have any desired number of tube segments depending on the outputto be produced, and these tube segments may be arranged in parallel orin series with each other; 2 and 3 denote a total reflection mirror andan output mirror, respectively, which are accurately positioned; and 4denotes an outgoing laser beam. The segments of the discharge tube areprovided with inlet and outlet ports connected to a single Roots blower7, and heat exchangers 5 and 6 are used to cool a laser gas heated bythe electric discharge and the compressing action of the Roots blower 7.The laser gas flows in the discharge tube 1 and gas delivery tubes inthe directions indicated by the arrows. The gas flows in the dischargetube 1 at the speed of about 100 m/second. Electrodes 8a, 8b to 11a, 11bare connected to respective high-frequency power supplies 12, 13, 14,and 15, and an electric discharge is produced by a high-frequencyvoltage from the high-frequency power supplies 12 to 15, to generatelaser oscillation.

In this type of high-frequency discharge pumped laser device havingplural discharge tube segments driven by respective independenthigh-frequency power supplies, the laser output fluctuates in the cycleof several hertz. This laser output fluctuation is illustrated in FIG.7, wherein time is indicated along the horizontal axis and the laseroutput is indicated along the vertical axis. As seen from FIG. 7, alaser output of about 1,000W is subject to an approximately 30Wfluctuation.

DISCLOSURE OF THE INVENTION

The object of the present invention is to solve the above-mentionedproblems and provide a high-frequency discharge pumped laser devicehaving a reduced output fluctuation and thus capable of stablehigh-frequency discharge pumping.

To solve the aforementioned problems, the present invention provides ahigh-frequency discharge pumped laser device for producing a laseroscillation through application of a high-frequency voltage to adischarge tube, comprising

a plurality of tube segments constituting the discharge tube,

high-frequency power supplies for supplying a high frequency voltage torespective tube segments, and

a partition wall made of an electroconductive material and arrangedbetween adjacent tube segments, a potential of the partition wall beingmaintained at a constant level.

The aforementioned problems are caused by a mutual current produced by astray capacity between the discharge tube segments, and the influence ofthe current is eliminated by arranging the partition wall between thetube segments and maintaining the potential of the wall at a constantlevel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an arrangement according to one embodiment of thepresent invention;

FIG. 2 is a diagram of an arrangement according to another embodiment ofthe present invention;

FIG. 3 is a conceptual diagram of the first embodiment;

FIG. 4 is an equivalent circuit diagram of FIG. 3;

FIG. 5 is a chart showing a laser output fluctuation according to thepresent invention;

FIG. 6 is a diagram of a prior art axial-flow type high-frequencydischarge pumped laser device;

FIG. 7 is a chart showing a laser output fluctuation according to theprior art high-frequency discharge pumped laser shown in FIG. 6;

FIG. 8 is a diagram for explaining the current flow between dischargetube segment of the prior art device shown in FIG. 6; and

FIG. 9 is an equivalent circuit diagram of FIG. 8.

BEST MODE OF CARRYING OUT THE INVENTION

Embodiments of the present invention will be described with reference tothe drawings.

First, an interference between the discharge tube segments will beexplained, with reference to FIG. 8, which is a diagram for explaining acurrent flow between tube segments arranged in parallel with each other.As shown in FIG. 8, discharge tube segments 1a and 1b are provided withelectrodes 8a, 8b and 9a, 9b, respectively, supplied with ahigh-frequency voltage from high-frequency power supplies 12 and 13. Ofdenotes a stray capacity between the tube segments 1a and 1b.

An equivalent circuit of FIG. 8 is illustrated in FIG. 9, wherein I₁represents the current flowing through the circuit of the high-frequencypower supply 12 in FIG. 8, I₂ represents the current flowing through thecircuit of the high-frequency power supply 13, I₀ represents theinterference current of these two circuits, Z₀ represents the impedanceof the stray capacity, and Z₁ and Z₂ represent the impedances of thedischarge tube segments 1a and 1b, respectively.

Voltages e1 and e2 of the high-frequency power supplies 12 and 13 aregiven by:

    e1=E.sub.1 sinω.sub.1 t

    e2=E.sub.2 sin(ω.sub.2 t+θ.sub.0)

where ω₁ represents the angular frequency of the high-frequency powersupply 12, ω₂ represents the angular frequency of the high-frequencypower supply 13, and θ₀ represents the phase difference between thesetwo power supplies.

Accordingly, the equation

    I.sub.1 =(Ia).sup.2 +(Ib).sup.2 +2IaIbcosθ.sub.1 ×sin {θ.sub.2 +tan.sup.-1 k}

stands, wherein ##EQU1## Therefore, the influence of the voltage e2 isapparent. Here, assuming that the connection by the stray capacity Z₀ isto be eliminated, i.e., Z₀ →∞, then

    Ib→0

    Ia→E.sub.1 /|Z.sub.1 |

and accordingly,

    I.sub.1 =E.sub.1 /|Z.sub.1 |sin(ω.sub.1 t+θ.sub.a1)

    θ.sub.a1 =Arg(1/Z.sub.1)

Therefore, the influence of the voltage e2 is eliminated.

From the above it will be noted that, by eliminating the stray capacitydirectly connecting the discharge tube segments 1a and 1b, theinterference between these tube segments 1a and 1b can be avoided.

FIG. 3 is a conceptual diagram of one embodiment of the presentinvention, and FIG. 4 is an equivalent circuit diagram thereof. In thesefigures, like reference symbols are used to denote like elements orparts shown in FIGS. 8 and 9. In FIG. 3, a partition wall B is arrangedbetween the discharge tube segments 1a and 1b and is connected at apoint P to a ground potential line of the high-frequency circuits. Thepartition wall B divides the stray capacity between the discharge tubesegments 1a and 1b into Cf1 and Cf2, as seen from the equivalent circuitdiagram of FIG. 4, and since the partition wall B is grounded, a pathfor passing the mutual current does not exist. Z₀₁ and Z₀₂ represent theimpedances of the stray capacities Cf1 and Cf2, respectively. As will beclear from the figures, ##EQU2## stand, and thus there is no influenceof the other voltage e2.

FIG. 1 shows an arrangement of the discharge tube according to oneembodiment of the present invention which is designed to be used in ahigh-frequency discharge pumped laser device such as that shown in FIG.8. In FIG. 1, the discharge tube segments 1a and 1b arranged in parallelto each other constitute a discharge tube, and these tube segments arepositioned in such a way that the axis of a laser beam can be passedcontinuously through these tube segments with the aid of a turningmirror or the like. Symbol B denotes the partition wall made of anelectroconductive material such as copper or aluminum and arranged inparallel to the tube segments 1a and 1b, and connected at a point P tothe ground potential line of the high-frequency power supplies 12 and13, and 16 denotes a support for supporting the tube segments 1a and 1b.The other necessary elements of a high-frequency discharge pumped laserdevice such as a total reflection mirror, output mirror, etc. aresimilar to those illustrated in FIG. 6.

Accordingly, as shown in FIG. 1, the partition wall B is arrangedbetween the parallel discharge tube segments 1a and 1b, and thusinterference between the segments 1a and 1b is prevented.

FIG. 2 shows a discharge tube arrangement according to anotherembodiment of the present invention also intended for use in a laserdevice such as that shown in FIG. 8. In the figure, the discharge tubeis constituted by segments 1a and 1b arranged in series, and a laserbeam is passed directly through the tube segments 1a and 1b. Thepartition wall B, made of an electroconductive material such as copperor aluminum, is arranged at right angles to the axis of the dischargetube segments 1a and 1b, and connected at a point P to the groundpotential line of the high-frequency power supplies 12 and 13. The otherelements are similar to those appearing in FIG. 6.

As shown in FIG. 2, the partition wall B is arranged between thedischarge tube segments 1a and 1b, which are positioned in series, andsince the partition wall B is grounded, interference between the tubesegments 1a and 1b is prevented.

FIG. 5 is a graph showing the laser output obtained with thearrangements of FIGS. 1 and 2. In the graph, time is indicated along thehorizontal axis, and the laser output is indicated along the verticalaxis. As illustrated, a laser output of about 1,000W fluctuates in therange of 3W or less, which is less than one-tenth of the range of laseroutput fluctuation illustrated in FIG. 7.

The foregoing description is based on the use of discharge tube segmentswhich are arranged in parallel or in series with each other, but similaradvantageous effects can be obtained with an arrangement wherein a setof series-connected discharge tube segments is located in parallel toanother set of similarly connected tube segments, by using the partitionwalls shown in FIGS. 1 and 2.

The aforementioned phenomena and effects were discovered for the firsttime by the inventor of the present application, and this invention wascreated to solve the problems peculiar to high-frequency dischargepumped laser devices of the type developed by the inventor, whichinclude individually driven discharge tube segments.

According to the present invention, as described above, a partition wallmade of an electroconductive material is provided between adjacentdischarge tube segments, and the potential thereof is maintained at aconstant level, whereby the interference between the discharge tubesegments is eliminated and thus fluctuation of the laser output isgreatly reduced.

I claim:
 1. A high-frequency discharge pumped laser device for producinga laser oscillation through application of a high-frequency voltage to adischarge tube, comprising:a plurality of adjacent tube segmentsconstituting the discharge tube; means for passing a laser gas axiallythrough each of said tube segments; a plurality of high-frequency powersupplies for supplying a high-frequency voltage to each one of said tubesegments to generate a laser beam output; a partition wall made of anelectroconductive material which is positioned between each of saidadjacent tube segments; and means connecting said partition wall to aground potential line of a high-frequency circuit to maintain thepotential of said partition wall at a constant level.
 2. Ahigh-frequency discharge pumped laser device according to claim 1,wherein said tube segments are arranged parallel to each other.
 3. Ahigh-frequency discharge pumped laser device according to claim 1,wherein said tube segments are arranged in series.